An apparatus is known (for example, Patent Document 1, etc.) in which an electrode connected to a power source and a grounded electrode are arranged, for example, in a vertical opposing relation, an atmospheric pressure plasma discharge space is formed between those electrodes and the substrate is set in this discharge space. The surface of each electrode for defining the discharge space is provided with a thermally sprayed film or plate composed of a solid dielectric for the purpose of stable discharge. Normally, the electrodes are firmly fixed to a holder of an apparatus main body so that no clattering occurs. Patent Document 2 discloses technique in which electrodes are loosely retained by a holder.    [Patent Document 1] Japanese Patent Application Laid-Open No. 2004-228136    [Patent Document 2] Japanese Patent Application Laid-Open No. H09-92493